This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Seven separate Lutheran mission churches operating across Tanganyika had cooperated loosely since 1938, a quarter century of informal federation before they formally united into a single body, the Evangelical Lutheran Church in Tanzania, on 19 June 1963. From that founding the united church grew at a sustained rate of around eight percent annually among its baptized members, an expansion pace few Christian bodies anywhere have matched over a comparable span of decades.
By 2020 that growth had carried membership to 7,916,253, roughly thirteen percent of Tanzania's entire population belonging to a single Lutheran church. The scale placed the Evangelical Lutheran Church in Tanzania as the second largest Lutheran church anywhere in the world and the largest found anywhere in East Africa, trailing only Ethiopia's Mekane Yesus church among Lutheran bodies globally.
What the 1963 union changed for Lutheranism's spread was consolidation into strength: seven mission churches too small individually to carry much weight became, once merged, one of the tradition's largest and fastest growing bodies anywhere, an East African counterpart to the comparable transformation already under way in Ethiopia during those very same decades of sustained growth.